The invention relates to a coil unit for inductive energy transfer, a vehicle having such a coil unit and a method for manufacturing the coil unit.
Induction charging systems are used for non-contact charging of an electrical energy storage device of a motor vehicle, such as, for example, a lithium-ion battery. For charging, the motor vehicle, in which a secondary induction coil is arranged, is to be placed for a relatively long period of time over a primary induction coil that acts as a charging apparatus, which emits a modulating magnetic field.
FIG. 1 shows, by way of example, a primary coil unit 1 arranged on or in the ground (e.g. road, parking lot, garage) and a secondary coil unit 3 arranged on the underbody of a vehicle 2. There is an air gap present between the primary and secondary coil units. On the one hand, the air gap should be as small as possible to achieve a high level of efficiency of the induction charging system and, on the other hand, it should be large enough in order not to present an obstacle for the vehicle 2, or cause damage due to the vehicle 2 driving over the primary coil unit.
FIG. 2 shows the induction charging system from FIG. 1 in somewhat more detail. In the primary coil unit 1 and the secondary coil unit 3, a primary induction coil 4 and a secondary induction coil 5 are provided accordingly that are each wrapped around a vertical axis and designed to be as flat as possible in a vertical direction so that the coil windings extend horizontally. The primary induction coil 4 is essentially constructed to be equal to the secondary induction coil 5, however vertically mirrored, wherein the primary induction coil 4 is typically larger than the secondary induction coil 5. Ferrite cores 6 are provided to guide the magnetic field lines. For the protection of the primary and secondary induction coils 4, 5, the coils are each embedded in a casting compound 7 composed of a magnetically neutral material.
FIG. 3 shows a cross-sectional top view of an induction coil, such as, for example, the primary induction coil 4 or the secondary induction coil 5. As an example, the coil can essentially be wound in a square or a round shape.
FIG. 4 shows a course of the magnetic field lines while the induction charging system is operating. The primary induction coil 4 generates a magnetic field, the magnetic field lines of which are drawn in FIG. 4. Several of the field lines run through both the primary as well as the secondary induction coil 4, 5, whereas other field lines only run through the primary induction coil 4. The amount of field lines that only run through the primary induction coil 4 must be kept as few as possible to achieve a good level of efficiency. For example, this is achieved by arranging ferrite cores 6 that guide the field lines.
The ferrite core 6 forms an important part of the respective coil unit 1, 3, which increases the inductance of the induction coil 4, 5 and/or focuses/guides the magnetic field. Ferrite is a ceramic substance that conducts electricity poorly or not at all. Similar to conventional ceramics, ferrite compounds are deemed to be fragile due to their brittle structure. The manufacturing process is based mostly on sintering processes, whereby only simple shapes can be made. For generating complex end contours, the simple geometric structures must be arranged next to each other in a row; for example, two plates arranged at a right angle result in an orthogonal component.
A disadvantage of this prior art is that the manufacturing of complex ferrite core geometric structures is not possible. There is the danger of cracking or breaking due to the brittle fracture properties of this material. In turn, such cracks worsen the inductive and magnetic properties of the coil unit. Specifically for induction charging systems, the induction coils and therefore the ferrite cores are relatively large and very flat at the same time. In the case of such a geometric structure, the brittle fracture properties of ferrite are unfavorable.
The object of the invention is to create a coil unit for inductive transfer of energy, which offers better protection against mechanical damage. This object is achieved by a coil unit, and a method of making the coil unit in accordance with embodiments of the invention.
In accordance with an exemplary embodiment of the invention, a coil unit for inductive energy transfer is provided with an induction coil and a ferrite core that interacts with the induction coil, wherein the ferrite core is made of a fiber-reinforced ceramic material. As a result, a one-piece ferrite core can be created, which is characterized by a high level of stability. The advantages of such a ferrite core are in the preservation of magnetic and inductive properties of the ferrite core, even when subjected to high loads. In addition, with regard to force distribution, the ferrite core can be integrated within a supporting underbody structure of the vehicle. Furthermore, a reduction of the manufacturing costs could be achieved due to reducing the number of components, in the case of complex 3D structures in particular. Due to the optimized shape of the ferrite core, an improved system behavior can be expected, meaning a higher level of efficiency, better performance, etc. In addition, the robustness of the ferrite core increases the service life. Furthermore, due to the adapted shape, a reduction in weight and installation space can be achieved.
In accordance with a further exemplary embodiment of the invention, the fibers in the fiber-reinforced ceramic material are electrically non-conductive or insulated against each other.
In accordance with a further exemplary embodiment of the invention, the fibers in the fiber-reinforced ceramic material are carbon fibers.
In accordance with a further exemplary embodiment of the invention, the fibers in the fiber-reinforced ceramic material are glass fibers.
In accordance with a further exemplary embodiment of the invention, the fibers in the ceramic material are embedded in a slidable manner.
In accordance with a further exemplary embodiment of the invention, the fibers within a ferrite core are unidirectionally aligned.
Furthermore, the invention makes a vehicle having such a coil unit available.
In addition, an exemplary embodiment of the invention provides a method for manufacturing a coil unit for inductive energy transfer comprising the following acts: Sintering of a ferrite core, wherein, during the sintering process, fibers are pressed into a ceramic material; provision of an induction coil and attachment of the induction coil relative to the ferrite core. Using the method according to the invention, the aforementioned advantages associated with the apparatus according to the invention can be achieved.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.